package com.jzoffer2;

import java.util.Scanner;

/**
 * TODO
 *
 * @author lefly
 * @version 1.0
 * @classname No64
 * @description
 * @date 2021/3/8 下午6:42
 */
public class No64 {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int input = sc.nextInt();
        int sum = sumNums(input);
        System.out.println(sum);

    }

    public static int sumNums(int n) {
        int sum = n;
        boolean flag = n > 0 && (sum += sumNums( n - 1)) > 0;
        return sum;
    }

}
